JP6351251B2 - Fixing apparatus and image forming apparatus including the fixing apparatus - Google Patents

Description

  The present invention relates to a fixing device (fixing device) mounted on an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer, and an image forming apparatus including the fixing device.

  In electrophotographic copying and printers, a toner image corresponding to image data is transferred to a recording material such as recording paper or an OHP sheet, and then the toner image transferred to the recording material is heated and pressed by a fixing device. Has been established.

  As the fixing device, there has been proposed a device using a cylindrical heat generating fixing belt (hereinafter referred to as a cylindrical rotating body) having a resistance heat generating layer that generates heat when an electric current flows (Patent Document 1, Patent). Reference 2).

  Patent Document 1 discloses a nip by pressing a pressure roll onto a cylindrical rotating body having a resistance heating layer formed by dispersing carbon nanomaterials and filamentary metal particles in a heat-resistant resin such as polyimide. A fixing device for forming a portion is disclosed. In Patent Document 2, a pressure roll is brought into pressure contact with a cylindrical rotating body having a resistance heating layer formed by dispersing a conductive filler and high-ion conductor powder in a heat-resistant resin such as polyimide. A fixing device for forming a nip portion is disclosed.

  In the fixing devices disclosed in Patent Document 1 and Patent Document 2, since the heat capacity of the cylindrical rotating body is small, the warm-up time is shortened, and it is possible to maintain a predetermined fixing temperature with a low amount of power. As a result, the toner image can be thermally fixed on the recording material at a high speed and with a low power consumption.

  In the above cylindrical rotating body, it is known that when breakage occurs so as to block the direction of the current flowing through the cylindrical rotating body, heat is concentrated at the damaged end portion, and the temperature rises locally ( (See paragraph number [0005] of Patent Document 2 and paragraph number [0021] of Patent Document 3). The local temperature rise of the cylindrical rotating body may cause image problems such as image unevenness and hot offset. In order to prevent the occurrence of image defects, it is better to detect the breakage of the cylindrical rotating body as soon as possible and warn of countermeasures such as device replacement.

  As a means for detecting damage to a cylindrical rotating body, a method of detecting an abnormal temperature rise of a cylindrical rotating body using a temperature detection element has been conventionally known (Patent Document 4). However, if the cylindrical rotating body rotates at a high speed, the response of the temperature detecting element cannot catch up, and the abnormal temperature rising portion may not be detected directly.

JP 2011-145656 A JP 2011-248098 A Japanese Patent No. 4650166 JP 2010-134035 A

  In a fixing device having a cylindrical rotating body that generates heat when energized, if the breakage occurs so as to block the direction of the current flowing through the cylindrical rotating body, it is required to detect the breakage during rotation of the cylindrical rotating body. ing.

SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device that is small in size, has high power conversion efficiency , and suppresses image problems , and an image forming apparatus including the fixing device.

(1) In order to achieve the above object, a fixing device according to the present invention includes:
A cylindrical rotating body having a conductive layer, and an alternating body that is arranged inside the rotating body and has a spiral-shaped portion whose spiral axis is substantially parallel to the generatrix direction of the rotating body, and causes the conductive layer to generate electromagnetic induction heat. A coil for forming a magnetic field, a magnetic core disposed along the generatrix direction in the spiral-shaped part, for inducing magnetic lines of the alternating magnetic field, and a pressure forming a nip part together with the rotating body A fixing device for fixing the image to the recording material by heating while conveying the recording material carrying the image at the nip portion,
The magnetic core is made of a ferromagnetic material and has a shape that does not form a loop outside the rotating body,
The sum of the permeance of the conductive layer and the permeance of the region between the conductive layer and the magnetic core is 28% or less of the permeance of the magnetic core;
Wherein a rotator temperature detecting member for detecting the temperature of the fluctuation amount of the rotating body 1 rotation period of the detected temperature of said temperature detecting member is stopped a predetermined amount larger field case, energization of the rotary body And

(2) In order to achieve the above object, the fixing device according to the present invention includes:
A cylindrical rotating body having a conductive layer, and an alternating body that is arranged inside the rotating body and has a spiral-shaped portion whose spiral axis is substantially parallel to the generatrix direction of the rotating body, and causes the conductive layer to generate electromagnetic induction heat. A coil for forming a magnetic field, a magnetic core disposed along the generatrix direction in the spiral-shaped part, for inducing magnetic lines of the alternating magnetic field, and a pressure forming a nip part together with the rotating body A fixing device for fixing the image to the recording material by heating while conveying the recording material carrying the image at the nip portion,
The magnetic core is made of a ferromagnetic material and has a shape that does not form a loop outside the rotating body,
The sum of the permeance of the conductive layer and the permeance of the region between the conductive layer and the magnetic core is 28% or less of the permeance of the magnetic core;
The has a temperature detecting member for detecting a temperature of the rotating body, the fluctuation amount of the rotating body 1 rotation period of the detected temperature of said temperature detecting member is characterized by notifying a predetermined amount greater than field case, the abnormality.
(3) In order to achieve the above object, an image forming apparatus according to the present invention includes:
In an image forming apparatus having an image forming unit that forms an image on a recording material, and a fixing unit that fixes an image formed on the recording material to the recording material.
The fixing unit includes the fixing device described in (1) or (2) above.

According to the present invention, it is possible to provide a fixing device that is small in size, has high power conversion efficiency , and suppresses image adverse effects , and an image forming apparatus including the fixing device.

Flow chart showing film breakage detection method and image forming apparatus operation of fixing device according to reference example Cross section of image forming apparatus Sectional view of a fixing device according to a reference example Front view of fixing device according to reference example Temperature transition diagram of film in fixing device according to embodiment 1 Diagram explaining abnormal temperature rise phenomenon when there is film breakage Illustration of film surface temperature due to different length of film breakage Block diagram of printer control unit of fixing device according to reference example Sectional view of the fixing device according to the first embodiment . 1 is a front view of a fixing device according to a first embodiment . Perspective view of heat generation layer, magnetic core and excitation coil of film of fixing device according to reference example Illustration of the heat generation principle of the heat generation layer Temperature transition diagram of film in fixing device according to embodiment 1 Diagram explaining abnormal temperature rise phenomenon when there is film breakage Graph of experimental results in Table 1 FIG. 6 is a diagram for explaining the arrangement position of the temperature detecting element in the fixing device according to the first embodiment . The figure explaining the abnormal temperature rise phenomenon when there is film breakage in the fixing device of another form of the reference example FIG. 2 is a schematic diagram of a heat generation layer, a magnetic core, an exciting coil, and magnetic lines of force in the fixing device according to the first embodiment , and a diagram of the magnetic core when a closed magnetic path is formed. Schematic diagram of a structure with a finite length solenoid Magnetic equivalent circuit diagram of space including magnetic core, excitation coil, and film per unit length Equivalent circuit of magnetic core and gap Coil and film equivalent circuit Illustration of circuit efficiency Diagram of experimental device used for measurement experiment of power conversion efficiency Results of measuring the magnetic flux ratio and conversion efficiency of the cylindrical rotating body The figure which arranged the temperature detection member inside the conductive layer of the film in the structure of the film, the magnetic core, and the nip forming member Sectional view of the structure shown in FIG.

Following, embodiments of the present invention will be described with reference to the drawings. Although the preferred embodiment of the present invention is an example of the best embodiment of the present invention, the present invention is not limited by the following examples, and other known configurations are within the scope of the idea of the present invention. It is possible to replace with.

[Reference example]
(1) Image forming apparatus 100
Referring to FIG. 2, for explaining an image forming apparatus equipped with Fixing device. FIG. 2 is a cross-sectional view showing a schematic configuration of an example of an image forming apparatus (monochrome printer in the present reference example ) 100 using an electrophotographic recording technique.

  In the image forming apparatus 100, an image forming unit 100A that forms a toner image on a recording material P includes a photosensitive drum 101 as an image carrier, a charging member 102, a laser scanner 103, and a developing device 104. Further, the image forming unit 100 </ b> A includes a cleaner 111 that cleans the photosensitive drum, and a transfer member 108. Since the operation of the image forming unit 100A is well known, detailed description thereof is omitted.

  The recording material P stored in the cassette 105 in the image forming apparatus main body 100 </ b> B is fed out one by one as the roller 106 rotates. The recording material P is conveyed to a transfer nip portion 108 </ b> T formed by the photosensitive drum 101 and the transfer member 108 by the rotation of the roller 107. The recording material P onto which the toner image has been transferred at the transfer nip portion 108T is sent to a fixing device (fixing portion) 110 via a conveyance guide 109, and the toner image is heated and fixed to the recording material by the fixing device. The recording material P exiting the fixing device 110 is discharged to the tray 113 by the rotation of the roller 112.

(2) Fixing device 110
With reference to FIGS. 3 and 4, the fixing device 110 of this reference example will be described. FIG. 3 is a cross-sectional view illustrating a schematic configuration of an example of the energization / heating type fixing device 110 according to the reference example . FIG. 4 is a front view showing a schematic configuration from the recording material conveyance side of the fixing device 110 shown in FIG.

  The pressure roller 8 as a pressure member includes a cored bar 8a, a heat-resistant elastic material layer 8b formed on the outer periphery between the shafts in the longitudinal direction of the cored bar, and a separation formed on the outer periphery of the elastic material layer. Mold layer (surface layer) 8c. Here, the longitudinal direction refers to a direction perpendicular to the recording material conveyance direction a. As a material of the elastic material layer 8b, a material having good heat resistance such as silicone rubber, fluorine rubber, and fluorosilicone rubber is preferable. The shaft portions on both sides in the longitudinal direction of the cored bar 8a are rotatably supported by a frame (not shown) of the apparatus via a bearing.

  A nip forming member 6 and a stay 5 as a reinforcing member are inserted into a cylindrical film 1 as a cylindrical rotating body. The nip portion forming member 6 is formed of a heat resistant resin material such as PPS, and faces the pressure roller 8 with the film 1 interposed therebetween. The stay 5 disposed on the nip portion forming member 6 is supported by the frame described above at the left end and the right end in the longitudinal direction of the stay.

Pressure springs 17a and 17b are contracted between spring receiving members 18a and 18b (see FIG. 4) provided on the frame at the left end and the right end of the stay 5, and a nip portion forming member is formed by the pressure spring. 6 is pressed in a direction perpendicular to the generatrix direction of the pressure roller 8. In this reference example , a pressing force having a total pressure of about 100 N to 250 N is applied to the nip portion forming member 6. The elastic material layer 8b of the pressure roller 8 is crushed and elastically deformed by the pressing force of the pressure springs 17a and 17b, and a nip N having a predetermined width is formed between the surface of the film 1 and the surface of the pressure roller (see FIG. 3A). ) Is formed.

  The pressure roller 8 is rotated by the motor M in the arrow direction (see FIG. 3A). The film 1 rotates in the direction of the arrow (see FIG. 3A) following the rotation of the pressure roller 8 while the inner surface of the film is in contact with the nip forming member 6.

  A flange member 12a is mounted on the left end side in the longitudinal direction of the nip portion forming member 6, and a flange member 12b is mounted on the right end side (see FIG. 4). When the film 1 rotates, the flange member 12a receives the left end portion of the film when the film moves to the left in the longitudinal direction, and serves to regulate the movement of the nip portion forming member 6 in the longitudinal direction. When the film 1 rotates, the flange member 12b receives the right end portion of the film when the film moves to the right side in the longitudinal direction, and serves to regulate the movement of the nip portion forming member 6 in the longitudinal direction.

  The position of the flange member 12a with respect to the film 1 is regulated by the regulating member 13a, and the position of the flange member 12b is regulated by the regulating member 13b. Each regulating member 13a, 13b is supported by a frame.

  As the material of the flange members 12a and 12b, materials having good heat resistance such as phenol resin, polyimide resin, polyamide resin, polyamideimide resin, PEEK resin, PES resin, PPS resin, fluorine resin, LCP resin, and mixed resins thereof can be used. preferable. PFA, PTFE, FEP, etc. are used as the fluororesin. LCP is a liquid crystal polymer.

  The flange members 12a and 12b also function as electrode members for supplying power to a heat generating layer 1a (described later) of the film 1. A conductive material (not shown) such as Ag is applied to the surfaces of the flange members 12a and 12b that are in contact with the film 1, and also plays a role of conducting alternating current to the film.

The film 1 has a diameter of about 10 to 50 mm. As shown in FIG. 3B , the film 1 has a heat generation layer (conductive layer) 1a as a base layer having a thickness of 30 to 200 μm, an elastic layer 1b formed on the outer surface of the heat generation layer, and an outer surface of the elastic layer. And a release layer 1c formed on the substrate.

  In the heat generating layer 1a, a carbon nanomaterial (not shown) and filamentous metal fine particles (not shown) are substantially uniformly dispersed in a matrix resin made of polyimide. The flange members 12a and 12b as electrode members are brought into contact with both ends of the heat generating layer 1a, and an alternating current is applied from the AC power source A through these flange members, thereby energizing in a direction perpendicular to the rotation direction of the film 1. The heat generating layer generates heat. The heat of the heat generating layer 1a is transmitted to the elastic layer 1b and the release layer 1c, and the entire film 1 is heated.

  As shown in FIGS. 3A and 4, the temperature detection of the film 1 is performed as a temperature detection member disposed at a position facing the film 1 on the side where the recording material P is conveyed to the fixing device 110. This is performed by the temperature measuring elements 9, 10, 11 of the non-contact type thermistor. The temperature measuring element 9 is arranged at the center in the longitudinal direction of the film 1, the temperature measuring element 10 is arranged at the left end in the longitudinal direction of the film 1, and the temperature measuring element 11 is arranged at the right end in the longitudinal direction of the film 1. These three temperature measuring elements 9, 10, and 11 detect temperatures at different positions in the direction of the rotation axis X (see FIG. 6) of the film 1, respectively.

The heat fixing processing operation of the fixing device 110 of this reference example will be described. The fixing device 110 of this reference example rotates the pressure roller 8 in the direction of the arrow by the motor M (see FIG. 3A) in response to a print command. The film 1 rotates in the direction of the arrow following the rotation of the pressure roller 8 while the inner surface of the film is in contact with the nip forming member 6. Further, the energization control unit 304 (see FIG. 8) is activated in response to the print command. Thereby, an alternating current is applied to the heat generating layer 1a of the film 1 from the AC power source A through the flange member 12b, the heat generating layer 1a of the film generates heat, and the temperature of the film rapidly rises.

  The detected temperatures of the temperature measuring elements 9, 10, and 11 for monitoring the surface temperature of the film 1 are output to the fixing temperature control unit 303 (see FIG. 8). The fixing temperature control unit 303 outputs the temperature detected by the temperature measuring element 9 at the center in the longitudinal direction of the film 1 to the engine control unit 302 (see FIG. 8). The engine control unit 302 controls the energization control unit 304 based on the temperature detected by the temperature measuring element 9 from the fixing temperature control unit 303. Thus, the film 1 is energized, and the surface temperature of the film is maintained and adjusted to a predetermined temperature adjustment target temperature (target temperature).

  While the recording material P carrying the unfixed toner image T is nipped and conveyed at the nip portion N, the heat and nip pressure of the film 1 are applied to the toner image, whereby the toner image is heated and fixed on the recording material.

(3) Temperature change in one rotation period of film (rotation period of one rotating body) due to film breakage FIG. 5 shows a temperature control target temperature at which the fixing device 110 is started and the unfixed toner image T on the recording material P can be fixed. The temperature transition of the film 1 in the process of heating up to is shown. The temperature transition shown in FIG. 5 is a temperature transition in a state in which the film 1 rotates following the rotation of the pressure roller 8. In FIG. 5, the alternate long and short dash line represents the temperature transition when no film breakage has occurred. The solid line represents the temperature transition at the film breakage end B and the film breakage end C (see FIGS. 6C and 6D) when the film breakage occurs so as to block the direction of the current flowing through the film 1. Yes.

  As is clear from FIG. 5, when there is no film breakage (one-dot chain line), there is no abrupt fluctuation, whereas when film breakage occurs (solid line), the film 1 corresponds to one rotation cycle of the film 1. Large fluctuations in surface temperature.

  FIGS. 6C and 6D are diagrams for explaining a phenomenon in which the surface temperature of the film fluctuates in one rotation cycle of the film when the film is broken. 6 (c) and 6 (d), arrows indicate the direction of current and the current density. Here, the rotation period of the film 1 refers to a period during which the film 1 rotates once.

  As described above, when an alternating current is applied through the flange members 12a and 12b, the alternating current is applied to the film 1 in the direction perpendicular to the rotation direction of the film as shown in FIGS. 6 (a) and 6 (b). Current flows. However, as shown in FIGS. 6C and 6D, when the film breakage occurs, the current flowing in the direction perpendicular to the rotation direction of the film 1 is bypassed at the film breakage end B or the film breakage end C. The current concentrates on these film break edges.

  When current flows from left to right with respect to the rotation direction of the film 1 as shown in FIG. 6C, the current that bypasses the film breakage end B or the film breakage end C does not return to the original path. It passes through a path close to the electrode member on the right side which is low as resistance, that is, the flange member 12b (not shown). Therefore, the current density is high (dense state) in the region from the vicinity of the film break ends B and C of the film 1 to the flange member 12b. On the other hand, in the region from the vicinity of the film break ends B and C of the film 1 to the left electrode member, that is, the flange member 12a (not shown), the current density is low (sparse state). When the current flows from right to left with respect to the rotation direction of the film 1 as shown in FIG. 6D, the current density with respect to the rotation direction of the film 1 is in the same state as in FIG.

  Therefore, when the time average of the film 1 rotation period of the film 1 of FIGS. 6 (c) and 6 (d) is taken, the current is bypassed and the current is locally degenerated in the entire film length where the film is broken. In this case, the current density is lowered and the temperature is lowered. As a result, as described above, the film surface temperature fluctuates over the entire length of the film 1 in one rotation period of the film.

(4) Sleeve Breakage Detection Method Based on Temperature Transition of Film 1 Rotation Period Next, a film breakage detection method based on the temperature transition of the film 1 rotation period of this reference example will be described. FIG. 7 is a schematic diagram showing the difference in the surface temperature of the film 1 depending on the magnitude of the film breakage in the time for two rotations of the film. In FIG. 7, the distance between film breaks in the film rotation direction (referring to the distance between the film break end B and the film break end C in the rotation direction of the film 1 shown in FIG. 6C) is the break length. .

  As is clear from FIG. 7, when the breakage length is long, as compared with the case where the breakage length is short, the time when the film is not broken (hereinafter, referred to as a reference temperature) T0 is lower than the time (FIG. 7). The middle tl) becomes longer. Considering the longitudinal direction of the film 1, the longer the breakage length of the current flowing in the direction perpendicular to the rotation direction of the film from both ends of the film shown in FIGS. This is because the current to be increased increases. This is because the region where the current density is low is increased when considered in the circumferential direction of the film 1.

  Further, when the breakage length is long, the temperature change amount (Tpp in the figure) of the film 1 becomes large. This is because the current density at the film breakage edge B and the film breakage edge C increases as the bypass current increases.

Using the above-described characteristics, in the fixing device 110 of this reference example, if the amount of temperature change (Tpp in FIG. 7) in one rotation period of the film is larger than a predetermined amount (predetermined value), an image defect may be caused. Judge. Then, the energization to the film 1 is stopped, or a notification that prompts the user to replace the device (notification of device abnormality) is given. Alternatively, when the time (t1 in FIG. 7) when the temperature is lower than the reference temperature T0 of one rotation period of the film is longer than a predetermined time (predetermined value), it is determined that there is a possibility of causing an image defect. Then, energization of the film 1 is stopped, or a notification for prompting the user to replace the device (notification of device abnormality) is given.

  FIG. 8 is a block diagram of the printer control unit 300. In the printer control unit 300, the printer controller 301 communicates with the host computer 311, receives image data, and develops the image data into information that can be printed by the printer. The printer controller 301 performs transmission / reception of signals and serial communication with an engine control unit 302 as a control unit.

  The engine control unit 302 transmits and receives signals to and from the printer controller 301, and further controls the fixing temperature control unit 303 and the energization control unit 304 via serial communication.

  The fixing temperature control unit 303 controls the temperature of the film 1 based on the temperature detected by the temperature measuring element 9 and detects an abnormal temperature of the film. The energization controller 304 controls the power applied to the film 1 by adjusting the input voltage of the AC power source A.

  In such a printer system having the printer control unit 300, the host computer 311 transfers the image data to the printer controller 301, and conversely captures the durable life information and warning information of the apparatus from the printer controller 301. The printer system includes an image forming apparatus 100 and a host computer 311 that can communicate with the image forming apparatus.

FIG. 1 is a flowchart showing a film breakage detection method of the fixing device 110 of this reference example and the operation of the image forming apparatus when film breakage is detected. A series of processing of Step 1-1 to Step 1-8 shown in FIG. 1 is stored in a memory (not shown) such as a ROM or RAM as a film breakage detection sequence, and starts up the fixing device 110 before reaching the temperature adjustment target temperature. Sometimes executed by the engine controller 302.

Step 1-1
As soon as the printer controller 301 fetches the print command, the engine control unit 302 drives the motor M and starts the start-up operation of the fixing device 110 so that the temperature adjustment target temperature is reached.

Step 1-2
At the same time when the start-up operation of the fixing device 110 is started, the fixing temperature control unit 303 rotates the film one time with the temperature measuring elements 9, 10, 11 at the center in the longitudinal direction, the left end portion in the longitudinal direction, and the right end portion in the longitudinal direction. Start monitoring the amount of change in the temperature of the cycle (the amount of change in temperature).

  Depending on the speed fluctuation of the motor M that rotationally drives the pressure roller 8 and the speed fluctuation caused by the eccentricity of the pressure roller 8 or the film 1, the rotation period of the film 1 may deviate from the ideal time. Alternatively, the rotation period of the film 1 may deviate from the ideal time due to a change in the frictional force between the pressure roller 8 and the film 1 within the circumference of the film, a change in the rotation speed of the film, or the like. In such a case, the rotation period of the film is set to a time considering a deviation from the ideal time of the rotation period of the film, and it is not necessary to strictly set the rotation period of the film.

Step 1-3
The engine control unit 302 determines whether or not the fluctuation amount of one rotation period of the film is equal to or less than a predetermined value. The fluctuation amount of the rotation period of the film 1 is calculated by the fixing temperature control unit 303 based on the temperature transition detected by the temperature measuring elements 9, 10, and 11.

  In any one of the temperature measuring elements 9, 10, and 11, when the fluctuation amount (Tpp in FIG. 7) of the rotation period of the film described above is larger than a predetermined value, the process proceeds to Step 1-6. When the fluctuation amount (Tpp in FIG. 7) of the rotation period of the film 1 is equal to or less than the predetermined value, the process proceeds to Step 1-4. Alternatively, when any of the temperature measuring elements 9, 10, and 11 has a time (t1 (variation amount) in FIG. 7) that is lower than the reference temperature T0 of one rotation period of the film longer than a predetermined time (predetermined value). Proceed to Step 1-6. When the time (t1 (fluctuation amount) in FIG. 7) that is lower than the reference temperature T0 of one rotation period of the film is equal to or shorter than a predetermined time (predetermined value), the process proceeds to Step 1-4. Here, the time t1 is a time during which the low temperature continues with respect to the reference temperature T0 of one rotation period of the film.

Step1-4
When the fluctuation amount of the rotation period of the film 1 is not more than a predetermined value, the fixing temperature control unit 303 determines whether or not the detected temperature of the temperature detecting element 9 at the center in the longitudinal direction of the film 1 has reached the temperature adjustment target temperature. When the temperature adjustment target temperature is not reached, the process returns to Step 1-3.

Step 1-5
When the fluctuation amount of the rotation period of the film is equal to or less than a predetermined value and the temperature detected by the temperature detecting element 9 reaches the temperature control target temperature, it is determined that the fixing device 110 can print, and the image forming apparatus 100 Print Ready is notified to a control unit (not shown).

Step 1-6
In Step 1-3, when the fluctuation amount of the rotation period of the film 1 is larger than a predetermined value, the fixing temperature control unit 303 determines that the film breakage may occur, which may cause image trouble, and engine control is performed to that effect. Notification to the unit 302.

Step 1-7
When it is determined that the film is broken, the engine control unit 302 immediately stops the power supply from the energization control unit 304 to the film 1.

Step 1-8
The printer controller 301 notifies the user of an abnormality in the fixing device 110 via the host computer 311. Alternatively, the abnormality of the fixing device 110 is notified to the user via an operation panel provided in the image forming apparatus main body 100A.

As described above, the fixing device 110 of this reference example has a plurality of temperature detecting elements 9, 10, and 11 in the longitudinal direction of the film 1, and based on the detected temperature of each of these temperature detecting elements, the film 1 rotation period. Monitor the amount of temperature fluctuation. If the amount of change in temperature during one rotation period of the film is greater than a predetermined value, it is determined that the film is broken. When it is determined that the film is damaged, the performance of the image forming apparatus 100 is brought out in order to stop the power supply to the film 1 or to notify the user of the abnormality of the apparatus before causing image problems such as image unevenness and hot offset. It becomes possible.

[Example 1]
Another example of the fixing device 110 will be described. The fixing device 110 shown in the present embodiment is an electromagnetic induction heating type device that heats and fixes an unfixed toner image T carried by the recording material P onto the recording material by the heat of a cylindrical film (sleeve) 21 that generates electromagnetic induction heat. is there.

(1) Fixing device 110
FIG. 9 is a cross-sectional view illustrating a schematic configuration of an example of the electromagnetic induction heating type fixing device 110 according to the present embodiment. FIG. 10 is a front view showing a schematic configuration of the fixing device 110 shown in FIG. 9 from the recording material conveyance side.

  The fixing device 110 according to the present exemplary embodiment includes a cylindrical film 21 as a cylindrical rotating body, a nip portion forming member 24, and a pressure roller 25 as a pressure member (opposing member). Furthermore, the fixing device 110 includes a magnetic core 22 as a magnetic core and an exciting coil 23 as a magnetic field generating unit inside the film 21.

  The nip portion forming member 24 is made of a heat resistant resin or the like. The nip portion forming member 24 is inserted into the film 21, and forms a nip portion N together with the pressure roller 25 on a flat surface 24a (see FIG. 9) on the pressure roller 25 side that contacts the inner surface of the film.

The film 21 has a cylindrical shape with a diameter of 10 mm to 50 mm. The layer structure of the film 21 includes a heat generating layer (conductive layer) 21a made of a conductive member serving as a base layer, an elastic layer 21b formed on the outer surface of the heat generating layer, and a release layer 21c formed on the outer surface of the elastic layer. It is a composite structure consisting of The material of the heat generating layer 21a is preferably a metal having a low volume resistivity. In this example, SUS having a thickness of 20 μm to 100 μm was used as the material of the heat generating layer 21a. As will be described later, the fixing device 110 of the present embodiment has a configuration in which a magnetic path is formed so as to circulate around the film 21, and therefore, a thin magnetic metal or a nonmagnetic metal that does not become a magnetic path is used as the heat generating layer 21a. Can do.

  On the outer surface of the heat generation layer 21a, a silicone rubber having a hardness of 20 degrees (JIS-A, 1 kg load) was formed as an elastic layer 21b with a thickness of 0.1 mm to 0.3 mm. The outer surface of the elastic layer 21b was covered with a fluororesin tube having a thickness of 10 μm to 50 μm as a release layer (surface layer) 21c.

  FIG. 11 is a perspective view showing the positional relationship among the heat generating layer 21 a of the film 21, the magnetic core 22, and the exciting coil 23 in the fixing device 110 according to the present embodiment.

As shown in FIG. 11, the magnetic core 22 formed in a columnar shape is substantially centered in the cross-sectional shape in the short direction of the film 21 (direction parallel to the conveyance direction “a” of the recording material P) by a fixing means (not shown). Is arranged. The magnetic core 22 functions as a member that guides the magnetic lines of force (magnetic flux) generated by the alternating magnetic field (alternating magnetic field) generated by the exciting coil 23 to the inside of the film 21 (inner surface side) and forms a path of magnetic lines of force (magnetic path). .

  The material of the magnetic core 22 is desirably formed of a material having a small hysteresis loss and a high relative permeability. As the material of the magnetic core 22, for example, a high permeability magnetic oxide such as sintered ferrite, ferrite resin, amorphous alloy or permalloy, or a ferromagnetic material made of an alloy material is preferable. The diameter of the magnetic core 22 is preferably as large as possible within a range that can be accommodated in the film 21, and the diameter is 5 mm to 40 mm. The shape of the magnetic core 22 is not limited to a cylindrical shape, and a polygonal column shape or the like can be selected.

  In the present embodiment, the magnetic core 22 is arranged only inside the film 21 to form an open magnetic path. However, as a modification of the present embodiment, the magnetic core 22 is circulated around the outside of the film. It is good also as a structure which arrange | positions and forms a closed magnetic circuit.

The exciting coil 23 intersects the rotation axis X of the film with a number of turns of about 10 to 30 turns of a single conductor of a copper wire having a diameter of 1 to 2 mm covered with a heat-resistant polyamideimide with respect to the magnetic core 22 inside the film 21. It has a spiral-shaped part formed by winding in the direction. The spiral axis 23X of the exciting coil 23 is substantially parallel to the direction of the rotation axis X of the film 21 (film bus direction) . Here, the spiral axis 23X refers to the center of the exciting coil 23 where the conductive wire is wound. In this embodiment, the exciting coil 23 is configured with 18 windings.

  As described above, the exciting coil 23 is formed by winding a single conducting wire around the magnetic core 22 in the direction crossing the direction of the rotation axis X of the film inside the film 21. For this reason, when a high-frequency current (alternating current) is passed through the excitation coil 23 via the power supply contact portions 23 a and 23 b, a magnetic field (magnetic field) is generated in a direction parallel to the direction of the rotation axis X of the film 21. That is, the magnetic core 22 is arranged in the exciting coil 23 which is arranged inside the film 21 and whose spiral axis line 23X is the direction of the rotation axis X of the film 21 to induce a magnetic field in the direction of the film rotation axis. The

  The pressure roller 25 has an outer diameter having a cored bar 25a, an elastic layer 25b formed on the outer surface between the shafts on both sides in the longitudinal direction of the cored bar, and a release layer 25c formed on the outer surface of the elastic layer. It is a 30 mm member.

  As shown in FIG. 10, a flange member 26a is mounted on the left end side in the longitudinal direction of the nip portion forming member 24, and a flange member 26b is mounted on the right end side. When the film 21 rotates, the flange member 26a receives the left end portion of the film when the film moves to the left side in the longitudinal direction, and serves to regulate the movement of the nip portion forming member 24 in the longitudinal direction. When the film 21 rotates, the flange member 26b receives the right end portion of the film when the film moves to the right side in the longitudinal direction, and serves to regulate the movement of the nip portion forming member 24 in the longitudinal direction.

  The position of the flange member 26a with respect to the film 21 is regulated by the regulating member 27a, and the position of the flange member 26b is regulated by the regulating member 27b. Each regulating member 27a, 27b is supported by a frame (not shown) of the apparatus.

  The fixing device 110 according to the present embodiment supports the left end portion and the right end portion in the longitudinal direction of the nip portion forming member 24 on the above-described frame, and the shaft portion of the core metal 25a of the pressure roller 25 is supported by the frame (not fixed). And is supported so as to be rotatable. Then, the nip portion forming member is placed between the spring receiving members 18a and 18b of the frame at the left end portion and the right end portion of the nip portion forming member 24 so that the nip portion forming member is aligned with the generatrix direction of the pressure roller 25. Pressing in the orthogonal direction.

  In the present embodiment, a pressing force of a total pressure of about 98 N to 196 N (about 10 kgf to about 20 kgf) is applied to the nip portion forming member 24. With this pressing force, the flat surface 24 a of the nip portion forming member 24 is pressed against the surface of the pressure roller 25 through the film 21. Thereby, the elastic layer 25b of the pressure roller 25 is crushed and elastically deformed, and a nip portion N having a predetermined width is formed between the surface of the film 21 and the surface of the pressure roller.

  The fixing heat treatment operation of the fixing device 110 of this embodiment will be described. The fixing device 110 of this embodiment rotates the pressure roller 25 in the direction of the arrow by the motor M in accordance with a print command (see FIG. 9). The film 21 rotates in the direction of the arrow following the rotation of the pressure roller 25 while the inner surface of the film is in contact with the flat surface 24 a of the nip portion forming member 24. In response to the print command, the energization control unit 304 starts up the high frequency converter 306 as a temperature control unit, and the high frequency converter supplies a high frequency current to the excitation coil 23 via the power supply contact portions 23a and 23b. Thereby, the heat generating layer 21a of the film 21 generates heat by electromagnetic induction, and the temperature of the film rapidly rises.

Output signals from the temperature measuring elements 9, 10, 11 that monitor the surface temperature of the film 21 are output to the fixing temperature control unit 303. The fixing temperature control unit 303 outputs the temperature detected by the temperature measuring element 9 at the center in the longitudinal direction of the film 21 to the engine control unit 302 (see FIG. 8). The engine control unit 302 controls the energization control unit 304 based on the temperature detected by the temperature measuring element 9 from the fixing temperature control unit 303. The energization control unit 304 controls the high-frequency converter 306, whereby the surface temperature of the film 21 is maintained and adjusted to a predetermined temperature adjustment target temperature (target temperature) .
While the recording material P carrying the unfixed toner image T is nipped and conveyed at the nip portion N, the heat and nip pressure of the film 21 are applied to the toner image, whereby the toner image is heated and fixed on the recording material.

  The heat generation principle of the film 21 will be described with reference to FIG. FIG. 12A is a schematic diagram showing the current flowing in the film 21 and the magnetic field generated in the film in the cross section in the short direction of the heat generating layer 21a. FIG. 12B is a schematic diagram showing the current flowing through the film 21 in the longitudinal direction of the heat generating layer 21a.

  FIG. 12 shows an example in which the magnetic core 22, the exciting coil 23, and the heat generating layer 21a are arranged concentrically from the center of the film 21 (see FIG. 12A). In the figure, the arrow magnetic field lines directed in the depth direction are simulated by Bin (× in the circle), and the arrow magnetic lines in the forward direction in the figure are simulated by Bout (• in the circle).

  At the moment when the current increases in the direction of the arrow I in the exciting coil 23, a magnetic field line is formed in the magnetic path as indicated by an arrow (X mark in the circle) directed in the depth direction in the figure. That is, there are eight magnetic lines Bin that go in the depth direction inside the magnetic core 22 that is inside the heat generating layer 21a, and there are eight magnetic lines Bout that return to the front side outside the heat generating layer 21a. When an alternating magnetic field is actually formed, an induced electromotive force is applied to the entire circumferential direction of the heat generating layer 21a so as to cancel the magnetic field lines formed in this way, and a current that flows around the film 21 flows as indicated by an arrow J (hereinafter, referred to as an arrow J). This current is called the circular current).

  Since the induced electromotive force is applied in the circulation direction of the heat generating layer 21a of the film 21, the circulating current J flows uniformly in the heat generating layer 21a. The lines of magnetic force generated from the magnetic core 22 repeat generation and disappearance and direction reversal due to the high-frequency current. Therefore, the circular current J repeats generation and disappearance and direction reversal in synchronization with the high-frequency current. When a current flows through the heat generating layer 21a, Joule heat is generated in the heat generating layer due to the electric resistance of the material (metal) of the heat generating layer.

  Joule heat generation is generally called “iron loss”, and the heat generation amount Pe is expressed by the following equation (1).

Pe: Heat generation amount t: Film thickness f: Frequency Bm: Maximum magnetic flux density ρ: Resistivity ke: Proportional constant Magnetic field lines generated from the magnetic core 22 are generated in parallel with the direction of the rotation axis X of the film 21 (see FIG. 11). The circulation current J flows in the circulation direction orthogonal to the direction of the rotation axis of the film.

  The circulating current J generated as described above depends on the magnetic flux contained in the magnetic core 22 and the resistance value of the heat generating layer 21a, and is not related to the magnetic flux density of the heat generating layer itself. Therefore, even a thin magnetic metal heating layer 21a that does not become a magnetic path or a nonmagnetic metal heating layer 21a can generate heat with high efficiency. Moreover, in the range where the resistance value of the heat generating layer 21a does not change extremely, it does not depend on the thickness of the material of the heat generating layer. Further, even when a conductive resin other than a metal material is used as the heat generating layer 21a, the heat generating layer can generate heat.

  That is, in the film 21 of this embodiment, an induction current is generated in the circumferential direction of the heat generating layer 21a by passing a high-frequency current through the exciting coil 23, and the heat generating layer generates heat by this induced current.

Since the configuration of the fixing device 110 of the present embodiment other than that described above is the same as that of the reference example , detailed description thereof is omitted.

(2) Temperature change in one rotation cycle of film due to film breakage FIG. 13 shows the film in the process of starting up the fixing device 110 and raising the temperature to the temperature control target temperature at which the unfixed toner image T on the recording material P can be fixed. The temperature transition of 21 is shown. The temperature transition shown in FIG. 13 is a temperature transition in a state where the film 21 rotates following the rotation of the pressure roller 25 as in the reference example . FIG. 14 is a diagram for explaining a phenomenon in which the surface temperature of the film fluctuates in one rotation cycle of the film when the film breakage occurs so as to block the current flowing through the film 21. In FIG. 14, arrows indicate the direction of current and the current density.
X is the rotation axis of the film 21.

  With reference to FIGS. 13 and 14, a description will be given of a temperature change in one rotation period of the film due to the film breakage of the film 21 in the fixing device 110 of the present embodiment.

In the fixing device 110 of this embodiment, the direction of the current flowing through the film 21 is parallel to the rotation direction of the film, unlike the reference example , as shown in FIG. 14 (actually an alternating current is applied). So there is also a current that flows in the opposite direction of the arrow). Therefore, as shown in FIG. 14, the circulating current flowing in the rotation direction of the film concentrates on the film break end D when the film break occurs in the direction of the rotation axis X of the film 21, and locally generates heat at the film break end. To do. Further, the temperature distribution of the film 21 is also different from that of the reference example .

In the fixing device 110 according to the reference example , a temperature change occurs in the film breakage edge B when the film 1 is broken or in the entire film length in the vicinity of the film breakage edge C. On the other hand, in the fixing device 110 of this embodiment, the film temperature in the region sufficiently separated in the longitudinal direction from the damaged portion of the film 21 due to the difference in the direction of the current flowing through the film 21 from the film 1 of the reference example. Unaffected by film damage.

  The dashed-dotted line shown in FIG. 13 is the temperature transition of the area | region sufficiently away from the area | region (area | region E shown in FIG. 14) where the film breakage has generate | occur | produced in the longitudinal direction of the film 21, like the area | region F in FIG. is there. On the other hand, the solid line shown in FIG. 13 represents the temperature transition of the film breakage end D in FIG. 14 when the film breakage occurs in the direction of blocking the current flowing through the film 21. Moreover, the broken line shown in FIG. 13 is a temperature transition of the area | region where the film breakage has generate | occur | produced like the area | region E in FIG.

  As is clear from FIG. 13, the film breakage edge (region D, solid line) has a large fluctuation of the film surface temperature according to one rotation cycle of the film 21. The area where the film breakage occurs (area E, broken line) is an area (area where the film breakage occurs) that is sufficiently separated from the area where the film breakage occurs due to the influence of the circulating current that bypasses the film break end D shown in FIG. F, the film surface temperature is lower than the one-dot broken line). Moreover, since it cannot energize in the area | region where the film breakage has generate | occur | produced, a film surface temperature is fluctuate | varied below according to 1 rotation period of a film.

  As an experimental example, the result of measuring the temperature fluctuation amount in one rotation period of the film is shown. An experiment was conducted using a film having a diameter of 30 mm and a length of 240 mm under the conditions of a temperature control target temperature of 160 ° C., a maximum input power of 1000 W, and a film rotation speed of 210 mm / sec.

  Table 1 shows the fluctuation of the temperature of one rotation cycle of the film depending on the difference in the film breakage length until the temperature control target temperature is reached (see FIG. 14) and the distance L from the film breakage end D (see FIG. 14). Represents the quantity result. Here, the fluctuation amount of the temperature of one rotation cycle of the film is the average temperature of the rotation cycle of the film as the reference temperature at a position sufficiently away from the film breakage edge D, and each position in Table 1. It is the difference between the film temperature and the maximum temperature of one rotation period of the film. Here, the position sufficiently away from the film breakage end D is the position of the temperature measuring element 9 at the center of the film 120 mm away from the film end D. That is, Table 1 shows a temperature change in which the temperature is raised at a temperature other than the temperature at which the film 21 generates heat when the normal fixing device is started up.

  FIG. 15 is a graph showing the results of Table 1. The results showed that the greater the film breakage length and the closer the longitudinal distance L from the film breakage edge D, the greater the temperature fluctuation in one rotation cycle of the film. In the fixing device 110 of the present embodiment, when the film is not damaged, the temperature unevenness in the longitudinal direction of the film 21 can be maintained within 8 ° C. in order to avoid the influence on the image uniformity due to the temperature unevenness on the film surface. It has become a structure. Therefore, if the longitudinal distance L from the film breakage end D of the film 21 is within 40 mm, it is possible to detect a film breakage having a film breakage length of 4 mm.

  FIG. 16 is a diagram for explaining the longitudinal positions of the three temperature measuring elements 9, 10, 11 of the present embodiment, which are arranged along the longitudinal direction of the film 21 based on the above results.

  In the fixing device 110 according to the present embodiment, the temperature measuring elements 10 and 11 are arranged at equally spaced positions separated by 80 mm from the temperature measuring element 9 arranged at the center position in the longitudinal direction of the film 21. As a result, even if the temperature measuring element is not disposed at a position directly opposite to the film damaged end D, any one of the three temperature measuring elements 9, 10, and 11 causes film damage occurring at an arbitrary position of the film 21. It can be detected from the fluctuation amount of the temperature of the rotation cycle.

  In the film 21 of this example, the heat resistance temperature of the elastic layer 21b made of silicone rubber and the release layer 21c made of a fluororesin tube formed on the outer surface of the elastic layer are both 230 ° C. The temperature control target temperature of the fixing device 110 is 160 ° C., and the maximum temperature of the film surface at the film break end D when the film breakage length is 4 mm is + 50 ° C. with respect to the case where there is no film breakage. Film breakage can be detected.

(3) Film Breakage Detection Method Based on Temperature Transition of One Rotation Period of Film The film breakage detection method in the fixing device 110 of this embodiment and the operation of the image forming apparatus when film breakage is detected are the fixing device 110 of the reference example. In the same manner as described above, the film breakage detection sequence is stored in the memory and executed by the engine control unit 302. Similarly to the first embodiment, the film breakage detection sequence of the present embodiment is also executed when the fixing device 110 is started up before reaching the temperature control target temperature. The film breakage detection sequence of the present example is Step 1-3 in FIG. 1, and uses the difference between the maximum temperature of the film rotation period and the reference temperature (average temperature) as the amount of change in the temperature of the film rotation period. Except for, it is the same as the reference example .

  As described above, the fixing device 110 according to the present exemplary embodiment includes the film 21 that generates heat by a current (circular current) flowing in a direction parallel to the rotation direction. The fixing device of this embodiment also has a plurality of temperature sensing elements 9, 10, and 11 in the longitudinal direction of the film 21, and monitors the amount of temperature fluctuation in one rotation period of the film based on the detected temperature of each of these temperature sensing elements. To do. If the amount of change in temperature during one rotation period of the film is greater than a predetermined value, it is determined that the film is broken. When it is determined that the film is damaged, the performance of the image forming apparatus 100 is brought out in order to stop the power supply to the film 1 or to notify the user of the abnormality of the apparatus before causing image problems such as image unevenness and hot offset. It becomes possible.

[Heat generation mechanism of fixing device 110 of this embodiment]
(1) Heat generation mechanism of fixing device 110 The heat generation mechanism of the fixing device 110 of this embodiment will be described with reference to FIG.

  Magnetic lines of force generated by passing an alternating current through the exciting coil 23 pass through the inside of the magnetic core 22 inside the cylindrical conductive layer in the direction of the generatrix (hereinafter referred to as the conductive layer) 21a of the heat generating layer (direction from S to N). Passes out from one end (N) of the magnetic core to the outside of the conductive layer and returns to the other end (S) of the magnetic core. As a result, an induced electromotive force is generated in the conductive layer that generates a magnetic force line in a direction that prevents increase or decrease in the magnetic flux penetrating the inside of the conductive layer 21a in the bus line direction of the conductive layer, and current is induced in the circumferential direction of the conductive layer. The conductive layer generates heat due to Joule heat generated by the induced current. The magnitude of the induced electromotive force V generated in the conductive layer 21a is proportional to the amount of change in magnetic flux per unit time (Δφ / Δt) passing through the inside of the conductive layer and the number of turns of the coil from the following equation (500). .

(2) Relationship between ratio of magnetic flux passing outside of conductive layer and power conversion efficiency The magnetic core 22 in FIG. 18A does not form a loop but has an end portion. The magnetic lines of force in the fixing device in which the magnetic core 22 forms a loop outside the conductive layer 21a as shown in FIG. 18B is induced by the magnetic core and exits from the inside to the outside of the conductive layer.

  However, in the case where the magnetic core 22 has an end portion as in the present embodiment, there is nothing that induces the lines of magnetic force emitted from the end portion of the magnetic core. For this reason, the path (N to S) in which the magnetic lines of force exiting one end of the magnetic core 22 return to the other end of the magnetic core includes an outer route passing outside the conductive layer 21a and an inner route passing inside the conductive layer. Both are likely to pass. Hereinafter, a route from N to S of the magnetic core 22 through the outside of the conductive layer 21a is referred to as an outer route, and a route from N to S of the magnetic core 22 through the inside of the conductive layer 21a is referred to as an inner route.

  The ratio of the magnetic force lines passing through the outer route out of the magnetic force lines coming out from one end of the magnetic core 22 has a correlation with the power consumed by the heat generation of the conductive layer 21a (power conversion efficiency) among the power input to the coil 23. It is an important parameter. As the ratio of the magnetic field lines passing through the outer route increases, the ratio of the power consumed by the heat generation of the conductive layer 21a (the power conversion efficiency) in the power input to the coil 23 increases.

  The reason is the same as the principle that the power conversion efficiency increases when the number of magnetic fluxes passing through the primary and secondary windings of the transformer is the same. That is, in this embodiment, the closer the number of magnetic fluxes passing through the inside of the magnetic core 22 and the number of magnetic fluxes passing through the outer route, the higher the power conversion efficiency, and the high-frequency current passed through the coil 23 is converted into the conductive layer. Therefore, electromagnetic induction can be efficiently performed as a circular current.

  This is because the magnetic field lines from S to N and the magnetic field lines passing through the inner route are opposite in the inside of the exciting core 22 in FIG. 18 (a), and therefore when viewed from the entire inner side of the conductive layer 21a including the magnetic core. These magnetic field lines will cancel each other. As a result, the number of magnetic lines of force (magnetic flux) passing through the entire inner side of the conductive layer 21a from S to N is reduced, and the amount of change in magnetic flux per unit time is reduced. When the amount of change in magnetic flux per unit time decreases, the induced electromotive force generated in the conductive layer 21a decreases, and the amount of heat generated in the conductive layer decreases.

From the foregoing, it is important for the fixing device 110 of this embodiment to manage the ratio of the magnetic field lines passing through the outer route in order to obtain the necessary power conversion efficiency.

(3) Index indicating the ratio of magnetic flux passing outside the conductive layer Therefore, the ratio of the magnetic field lines passing through the outer route in the fixing device 110 is expressed by using an index called permeance. First, the concept of a general magnetic circuit will be described. A circuit of a magnetic path through which magnetic lines of force pass is called a magnetic circuit with respect to an electric circuit. When calculating the magnetic flux in the magnetic circuit, it can be performed in accordance with the calculation of the electric circuit current. Ohm's law for electrical circuits can be applied to magnetic circuits. When the magnetic flux corresponding to the current of the electric circuit is Φ, the magnetomotive force corresponding to the electromotive force is V, and the magnetic resistance corresponding to the electric resistance is R, the following equation (501) is satisfied.

Φ = V / R (501)
However, here, in order to explain the principle more easily, a permeance P that is the reciprocal of the magnetic resistance R will be used. When the permeance P is used, the above equation (501) can be expressed as the following equation (502).

Φ = V × P (502)
Further, this permeance P can be expressed by the following equation (503), where B is the length of the magnetic path, S is the cross-sectional area of the magnetic path, and μ is the magnetic permeability of the magnetic path.

P = μ × S / B (503)
It is represented by The permeance P is proportional to the cross-sectional area S and the magnetic permeability μ, and is inversely proportional to the length B of the magnetic path.

FIG. 19A shows a magnetic core 22 having a radius a1 [m], a length B [m], and a relative permeability μ1 inside the conductive layer 1a, and a coil 23 with a helical axis as a generatrix direction of the conductive layer 21a. Is a diagram showing what is wound N [times] so as to be substantially parallel to. Here, the conductive layer 21a is a conductor having a length B [m], an inner diameter a2 [m], an outer diameter a3 [m], and a relative permeability μ2. The vacuum magnetic permeability inside and outside the conductive layer is μ ₀ [H / m]. Let the magnetic flux 8 generated per unit length of the magnetic core 22 when the current I [A] is passed through the coil 23 be φc (x).

  FIG. 19B is a cross-sectional view perpendicular to the longitudinal direction of the magnetic core 22. The arrows in the figure represent magnetic flux parallel to the longitudinal direction of the magnetic core 22 that passes through the inside of the magnetic core 22, the inside of the conductive layer 21a, and the outside of the conductive layer 21a when the current I flows through the coil 23. . The magnetic flux passing through the inside of the magnetic core 22 is φc (= φc (x)), the magnetic flux passing through the inside of the conductive layer 21a (the region between the conductive layer 21a and the magnetic core 22) is φa_in, and the magnetic flux passing through the conductive layer 21a itself. Let φs be the magnetic flux passing through the outside of the conductive layer 21a.

  FIG. 20A shows a magnetic equivalent circuit of a space including the core 22, the coil 23, and the conductive layer 21a per unit length shown in FIG. The magnetomotive force generated by the magnetic flux φc passing through the magnetic core 22 is Vm, and the permeance of the magnetic core 22 is Pc. Further, the permeance inside the conductive layer 21a is Pa_in, the permeance inside the conductive layer 21a itself of the film is Ps, and the permeance outside the conductive layer 21a is Pa_out.

  Here, when Pc is sufficiently larger than Pa_in and Ps, the magnetic flux that passes through the inside of the magnetic core 22 and exits from one end of the magnetic core passes through any one of φa_in, φs, and φa_out, and the magnetic core 2 It is thought that it returns to the other end. Therefore, the following relational expression (504) is established.

φc = φa_in + φs + φa_out (504)
Also, φc, φa_in, φs, and φa_out are expressed by the following equations (505) to (508), respectively.

φc = Pc × Vm (505)
φs = Ps × Vm (506)
φa_in = Pa_in × Vm (507)
φa_out = Pa_out · Vm (508)
Therefore, when (505) to (508) are substituted into the equation (504), Pa_out is expressed as the following equation (509).

Pc × Vm = Pa_in × Vm + Ps × Vm + Pa_out × Vm
= (Pa_in + Ps + Pa_out) × Vm
∴Pa_out = Pc−Pa_in−Ps (509)
From FIG. 19B, when the cross-sectional area of the magnetic core 22 is Sc, the cross-sectional area inside the conductive layer 21a is Sa_in, and the cross-sectional area of the conductive layer 21a itself is Ss, Pc is expressed as follows: It can be expressed by “magnetic permeability × cross-sectional area”, and the unit is [H · m].

Pc = μ1 · Sc = μ1 · π (a1) ² (510)
Pa_in = μ0 · Sa_in = μ0 · π · ((a2) ² − (a1) ² ) (511)
Ps = μ2 · Ss = μ2 · π · ((a3) ² − (a2) ² ) (512)
When these (510) to (512) are substituted into the equation (509), Pa_out can be expressed by the equation (513).

Pa_out = Pc−Pa_in−Ps
= Μ1 ・ Sc−μ0 ・ Sa_in−μ2 ・ Ss
= Π · μ1 · (a1) ²
-Π · μ0 · ((a2) ^2- (a1) ² )
-Π · μ2 · ((a3) ^2- (a2) ² ) (513)
By using the above equation (513), it is possible to calculate Pa_out / Pc, which is the ratio of the lines of magnetic force that pass outside the conductive layer 21a.

  Instead of the permeance P, a magnetic resistance R may be used. When discussing using the magnetic resistance R, since the magnetic resistance R is simply the reciprocal of the permeance P, the magnetic resistance R per unit length can be expressed by “1 / (permeability × cross-sectional area)”. The unit is “1 / (H · m)”.

Table 2 shows specific calculation results using parameters of the fixing device 110 of the present embodiment .

The magnetic core 22 is made of ferrite (relative magnetic permeability 1800), has a diameter of 14 [mm], and has a cross-sectional area of 1.5 × 10 ⁻⁴ [m ² ]. The nip portion forming member 24 is made of PPS (polyphenylene sulfide) (relative magnetic permeability 1.0) and has a cross-sectional area of 1.0 × 10 ⁻⁴ [m ² ]. The conductive layer 21a is made of aluminum (relative magnetic permeability 1.0), has a diameter of 24 [mm], a thickness of 20 [μm], and a cross-sectional area of 1.5 × 10 ⁻⁶ [m ² ].

  The cross-sectional area of the region between the conductive layer 21a and the magnetic core 22 is the cross-sectional area of the magnetic core and the cross-sectional area of the nip forming member 24 from the cross-sectional area of the hollow portion inside the conductive layer having a diameter of 24 [mm]. Calculated by subtracting. The elastic layer 21b and the release layer 21c are provided outside the conductive layer 21a and do not contribute to heat generation. Therefore, in the magnetic circuit model for calculating the permeance, it can be regarded as an air layer outside the conductive layer, so that it is not necessary to take into account.

  From Table 2, Pc, Pa_in, and Ps have the following values.

Pc = 3.5 × 10 ⁻⁷ [H · m]
Pa_in = 1.3 × 10 ⁻¹⁰ + 2.5 × 10 ⁻¹⁰ [H · m]
Ps = 1.9 × 10 ⁻¹² [H · m]
Using these values, Pa_out / Pc can be calculated from the following equation (514).

Pa_out / Pc = (Pc−Pa_in−Ps) /Pc=0.999 (99.9%) (514)
In some cases, the magnetic core 22 is divided into a plurality in the longitudinal direction, and a gap (gap) is provided between the divided magnetic cores. In this case, if the air gap is filled with air or a material whose relative permeability can be regarded as 1.0 or much smaller than the relative permeability of the magnetic core 22, the magnetic resistance R of the entire magnetic core increases and the magnetic field lines are reduced. The guiding function will deteriorate.

  The method of calculating the permeance of such a divided magnetic core 22 is complicated. Hereinafter, a method of calculating the permeance of the entire magnetic core when the magnetic core is divided into a plurality of pieces and arranged at equal intervals with a gap or a sheet-like nonmagnetic material in between will be described. In this case, it is necessary to derive the magnetic resistance of the entire length, divide it by the total length to obtain the magnetic resistance per unit length, and take the inverse to obtain the permeance per unit length.

  First, a longitudinal configuration diagram of the magnetic core is shown in FIG. The magnetic cores c1 to c10 have a cross-sectional area Sc, a magnetic permeability μc, and a width Lc per divided magnetic core, and the gaps g1 to g9 have a cross-sectional area Sg, a magnetic permeability μg, and a width Lg per gap. . The total magnetic resistance Rm_all in the longitudinal direction of the magnetic core is given by the following equation (515).

Rm_all = (Rm_c1 + Rm_c2 + ... + Rm_c10) +
(Rm_g1 + Rm_g2 + ... + Rm_g9) (515)
In the case of this configuration, since the shape, material, and gap width of the magnetic core are uniform, assuming that the sum total of Rm_c is ΣRm_c, and the sum total of Rm_g is ΣRm_g, the following equations (516) to ( 518).

Rm_all = (ΣRm_c) + (ΣRm_g) (516)
Rm_c = Lc / (μc · Sc) (517)
Rm_g = Lg / (μg · Sg) (518)
By substituting Equation (517) and Equation (518) into Equation (516), the total longitudinal magnetic resistance Rm_all can be expressed as in Equation (519) below.

Rm_all = (ΣRm_c) + (ΣRm_g)
= (Lc / (μc · Sc)) × 10 + (Lg / (μg · Sg)) × 9
... (519)
Here, the magnetic resistance Rm per unit length is expressed by the following equation (520), where ΣLc is the sum of Lc and ΣLg is the sum of Lg.

Rm = Rm_all / (ΣLc + ΣLg)
= Rm_all / (L × 10 + Lg × 9) (520)
From the above, the permeance Pm per unit length is obtained as in the following equation (521).

Pm = 1 / Rm = (ΣLc + ΣLg) / Rm_all
= (ΣLc + ΣLg) / [{ΣLc / (μc + Sc)} + {ΣLg / (μg + S
g)}]
... (521)
Increasing the gap Lg leads to an increase in magnetic resistance (decrease in permeance) of the magnetic core 22. In configuring the fixing device of the present embodiment, it is desirable to design the magnetic core 22 so that the magnetic resistance of the magnetic core 22 is small (permeance is large) from the viewpoint of heat generation. However, in some cases, the magnetic core 2 is divided into a plurality of gaps to prevent breakage of the magnetic core 22.

  From the above, it was shown that the percentage of magnetic field lines passing through the outer route can be expressed using permeance or magnetoresistance.

(3) Power Conversion Efficiency Required for the Fixing Device Next, power conversion efficiency required for the fixing device of this embodiment will be described. For example, when the power conversion efficiency is 80%, the remaining 20% of the power is converted into heat energy by a coil or core other than the conductive layer and consumed. When power conversion efficiency is low, things that should not generate heat, such as magnetic cores and coils, generate heat, and it may be necessary to take measures to cool them.

By the way, in this embodiment , when the conductive layer 21a generates heat, a high-frequency alternating current is passed through the exciting coil 22 to form an alternating magnetic field. The alternating magnetic field induces a current in the conductive layer 21a. The physical model is very similar to transformer magnetic coupling. Therefore, when considering the power conversion efficiency, an equivalent circuit of the magnetic coupling of the transformer can be used. The alternating magnetic field magnetically couples the exciting coil 22 and the conductive layer 21a, and the electric power supplied to the exciting coil is transmitted to the conductive.

  The “power conversion efficiency” described here is the ratio of the power input to the exciting coil 22 as the magnetic field generating means and the power consumed by the conductive layer 21a. In the case of the present embodiment, it is the ratio of the power input to the high-frequency converter 306 to the excitation coil 3 shown in FIG. 1 and the power consumed by the conductive layer 21a. This power conversion efficiency can be expressed by the following equation (522).

Power conversion efficiency = power consumed in the conductive layer / power supplied to the excitation coil (522)
The electric power supplied to the excitation coil 22 and consumed outside the conductive layer 21a includes a loss due to the resistance of the excitation coil and a loss due to the magnetic characteristics of the magnetic core material.

  FIG. 22 is an explanatory diagram regarding circuit efficiency. In FIG. 22A, 21a is a conductive layer, 22 is a magnetic core, and 23 is an exciting coil. FIG. 22B shows an equivalent circuit.

R1 is the loss of the exciting coil and magnetic core, L1 is the inductance of the exciting coil that circulates around the magnetic core, M is the mutual inductance between the winding and the conductive layer, L2 is the inductance of the conductive layer, and R2 is the resistance of the conductive layer . An equivalent circuit when the conductive layer is not mounted is shown in FIG. The device such as an impedance analyzer or LCR meter, equivalent series resistance from both ends of the exciting coil when measuring the R _1, equivalent inductance L _1, the impedance Z _A when viewed from the exciting coil ends can be expressed as equation (523).

Z _A = R ₁ + jωL ₁ (523)
Current flowing through the circuit is lost by R _1. That is, R1 represents a loss due to the coil and the magnetic core.

  An equivalent circuit when the conductive layer is mounted is shown in FIG. If the series equivalent resistances Rx and Lx when the conductive layer is mounted are measured, the relational expression (524) can be obtained by equivalent conversion as shown in FIG.

... (524)

... (525)

... (526)
M represents the mutual inductance between the exciting coil and the conductive layer.

  As shown in FIG. 23C, when the current flowing through R1 is I1 and the current flowing through R2 is I2, Expression (527) is established.

... (527)
Expression (528) can be derived from Expression (527).

... (528)
The efficiency (power conversion efficiency) is represented by Expression (529) because it is represented by the power consumption of the resistor R2 / (the power consumption of the resistor R1 + the power consumption of the resistor R2).

(529)
Series equivalent resistance R ₁ before attachment of the conductive layer, when measuring the equivalent series resistance Rx after mounting, of the power supplied to the exciting coil, power conversion indicating how much power is consumed by the conductive layer Efficiency can be calculated.

In this example , an impedance analyzer 4294A manufactured by Agilent Technologies was used for measuring the power conversion efficiency. First, a series equivalent resistance R ₁ of the winding ends measured in the absence of the fixing film was measured equivalent series resistance Rx from the winding ends in a state where the insertion of the magnetic core to the next fixing film.
R ₁ = 103 mΩ and Rx = 2.2Ω. At this time, the power conversion efficiency can be obtained as 95.3% by the equation (529). Thereafter, the power conversion efficiency is used to evaluate the performance of the fixing device.

  Here, the conversion efficiency of power required by the apparatus is obtained. The conversion efficiency of electric power is evaluated by changing the ratio of the magnetic flux passing through the outer route of the conductive layer 21a. FIG. 24 is a diagram illustrating an experimental apparatus used in a measurement experiment of power conversion efficiency.

The metal sheet 1S is an aluminum sheet having a width of 230 mm, a length of 600 mm, and a thickness of 20 μm. The metal sheet 1S is rolled into a cylindrical shape so as to surround the magnetic core 22 and the coil 23, and is made conductive by being conducted at the thick line 1ST portion. The magnetic core 22 is a ferrite having a relative permeability of 1800 and a saturation magnetic flux density of 500 mT, and has a cylindrical shape with a cross-sectional area of 26 mm ² and a length of 230 mm. The magnetic core 22 is arranged in the approximate center of the cylinder of the aluminum sheet 1S by fixing means (not shown). A coil 23 is spirally wound around the magnetic core 22 with 25 turns. When the end of the metal sheet 1S is pulled in the direction of the arrow 1SZ, the diameter 1SD of the conductive layer can be adjusted in the range of 18 to 191 mm.

  FIG. 25 is a graph in which the horizontal axis represents the ratio [%] of the magnetic flux passing through the outer route of the conductive layer, and the vertical axis represents the power conversion efficiency at a frequency of 21 kHz.

  The power conversion efficiency rapidly increases after plot P1 in the graph of FIG. 25 and exceeds 70%, and in the range R1 indicated by the arrow, the power conversion efficiency is maintained at 70% or more. In the vicinity of P3, the power conversion efficiency rapidly increases again, and is 80% or more in the range R2. In the range R3 after P4, the power conversion efficiency is stable at a high value of 94% or more. The reason why the power conversion efficiency has begun to rise rapidly is that the circulating current has efficiently started to flow through the conductive layer.

  Table 3 below shows the results of actually designing and evaluating the configuration corresponding to P1 to P4 in FIG. 25 as a fixing device.

(Fixing device P1)
In this configuration, the cross-sectional area of the magnetic core is 26.5 mm ² (5.75 mm × 4.5 mm), the diameter of the conductive layer is 143.2 mm, and the ratio of the magnetic flux passing through the outer route is 64%. The power conversion efficiency obtained by the impedance analyzer of this apparatus was 54.4%. The power conversion efficiency is a parameter indicating the amount of power input to the fixing device that contributes to heat generation of the conductive layer. Therefore, even if it is designed as a fixing device capable of outputting a maximum of 1000 W, about 450 W is a loss, and the loss is a heat generation of the coil and the magnetic core.

  In the case of this configuration, the coil temperature may exceed 200 ° C. even when 1000 W is applied for several seconds at startup. Considering that the heat resistance temperature of the coil insulator is in the latter half of 200 ° C. and that the Curie point of the magnetic core of ferrite is usually about 200 ° C. to 250 ° C., the loss of 45% makes the member such as the excitation coil below the heat resistance temperature It will be difficult to keep on. Further, when the temperature of the magnetic core exceeds the Curie point, the inductance of the coil is abruptly reduced, resulting in load fluctuation.

  Since about 45% of the power supplied to the fixing device is not used for heat generation of the conductive layer, it is necessary to supply about 1636 W to supply 900 W (assuming 90% of 1000 W) to the conductive layer. This is a power source that consumes 16.36 A at 100 V input. There is a possibility of exceeding the allowable current that can be input from the commercial AC attachment plug. Therefore, there is a possibility that the fixing device P1 having a power conversion efficiency of 54.4% may have insufficient power to be supplied to the fixing device.

(Fixing device P2)
In this configuration, the cross-sectional area of the magnetic core is the same as P1, the diameter of the conductive layer is 127.3 mm, and the ratio of the magnetic flux passing through the outer route is 71.2%. The power conversion efficiency obtained by the impedance analyzer of this apparatus is 70.8%. Depending on the specifications of the fixing device, the temperature rise of the coil and the core may be a problem.

  If the fixing device having this configuration is a high-spec device capable of printing operation at 60 sheets / minute, the rotational speed of the conductive layer is 330 mm / sec, and the temperature of the conductive layer needs to be maintained at 180 ° C. If it is attempted to maintain the temperature of the conductive layer at 180 ° C., the temperature of the magnetic core may exceed 240 ° C. in 20 seconds. Since the Curie temperature of the ferrite used as the magnetic core is usually about 200 ° C. to 250 ° C., the ferrite exceeds the Curie temperature, the permeability of the magnetic core decreases rapidly, and the magnetic field lines can be appropriately induced by the magnetic core. It may disappear. As a result, it may be difficult to induce a circulating current to generate heat in the conductive layer.

  Therefore, if the fixing device having the range R1 of the magnetic flux passing through the outer route is the above-mentioned high-spec device, it is desirable to provide a cooling means to lower the temperature of the ferrite core. As the cooling means, an air cooling fan, water cooling, a heat radiating plate, a heat radiating fin, a heat pipe, a Beltier element, or the like can be used. Of course, if this configuration does not require such high specifications, the cooling means is unnecessary.

(Fixing device P3)
In this configuration, the cross-sectional area of the magnetic core is the same as P1, and the diameter of the conductive layer is 63.7 mm. The power conversion efficiency required by the impedance analyzer of this apparatus is 83.9%. Although heat is constantly generated in the magnetic core and the coil, the cooling means is not at a necessary level.

  If the fixing device having this configuration is a high-spec device capable of printing at 60 sheets / minute, the rotational speed of the conductive layer is 330 mm / sec, and the surface temperature of the conductive layer may be maintained at 180 ° C., but the magnetic core ( The temperature of the ferrite does not rise above 220 ° C. Therefore, in this configuration, when the fixing device has the above-mentioned high specifications, it is desirable to use ferrite having a Curie temperature of 220 ° C. or higher.

  From the foregoing, it is desirable that the fixing device having the configuration in which the ratio of the magnetic flux passing through the outer route is in the range R2 is optimized for heat-resistant design such as ferrite when used at high specifications. On the other hand, such a heat-resistant design is not necessary when high specifications are not required for the fixing device.

(Fixing device P4)
In this configuration, the cross-sectional area of the magnetic core is the same as P1, and the diameter of the cylindrical body is 47.7 mm. The power conversion efficiency required by the impedance analyzer in this apparatus is 94.7%. Even if the surface temperature of the conductive layer is maintained at 180 ° C. with a high-spec device (the rotational speed of the conductive layer is 330 mm / sec) that can perform a printing operation of 60 sheets / min. Neither coils nor coils reach 180 ° C or higher. Therefore, a cooling means for cooling the magnetic core, the coil and the like and a special heat resistant design are unnecessary.

  As described above, in the range R3 in which the ratio of the magnetic flux passing through the outer route is 94.7% or more, the power conversion efficiency is 94.7% or more, and the power conversion efficiency is sufficiently high. Therefore, no cooling means is required even when used as a further high-spec fixing device.

  Further, in the range R3 where the power conversion efficiency is stable at a high value, even if the amount of magnetic flux per unit time passing through the inside of the conductive layer slightly varies due to the variation in the positional relationship between the conductive layer and the magnetic core. The amount of fluctuation in the power conversion efficiency is small, and the heat generation amount of the conductive layer is stabilized. In a fixing device in which the distance between the conductive layer and the magnetic core is likely to fluctuate, such as a flexible film, using the region R3 where the power conversion efficiency is stable at a high value has a great advantage. .

From the foregoing, it can be seen that the fixing device of this embodiment needs to have a ratio of magnetic flux passing through the outer route of 72% or more in order to satisfy at least the necessary power conversion efficiency. According to Table 3, the fixing device in the range R1 of this embodiment has a magnetic flux ratio of 71.2% that passes through the outer route of the conductive layer, but is 72% in consideration of measurement errors and the like.

(4) Relational expression of permeance or magnetoresistance to be satisfied by the device The ratio of the magnetic flux passing through the outer route of the conductive layer is 72% or more indicates that the permeance of the conductive layer and the inner side of the conductive layer (of the conductive layer and the magnetic core) This is equivalent to the fact that the sum of the permeance of the region in between is 28% or less of the permeance of the magnetic core. Accordingly, one of the characteristic configurations of this embodiment is that the following equation (529) is satisfied when the permeance of the magnetic core is Pc, the permeance inside the conductive layer is Pa, and the permeance Ps of the conductive layer is satisfied. It is.

0.28 × Pc ≧ Ps + Pa (529)
Further, when the permeance relational expression is replaced with a magnetic resistance, the following expression (530) is obtained.

... (530)
However, the combined magnetic resistance Rsa of Rs and Ra is calculated as in the following formula (531).

... (531)
Rc: Magnetoresistance of the magnetic core Rs: Magnetoresistance of the conductive layer Ra: Magnetoresistance of the region between the conductive layer and the magnetic core Rsa: Combined magnetoresistance of Rs and Ra The above permeance or magnetoresistance relation is fixed It is desirable that the cross section in the direction perpendicular to the generatrix direction of the cylindrical rotating body is satisfied throughout the maximum conveyance area of the recording material of the apparatus. Similarly, in the fixing device in the range R2 of this embodiment , the ratio of the magnetic flux passing through the outer route of the conductive layer is 92% or more.

According to Table 2, the fixing device in the range R2 of this embodiment has a magnetic flux ratio of 91.7% that passes through the outer route of the conductive layer, but is 92% in consideration of measurement errors and the like. The ratio of the magnetic flux passing through the outer route of the conductive layer is 92% or more indicates that the sum of the permeance of the conductive layer and the permeance of the inner side of the conductive layer (the region between the conductive layer and the magnetic core) is the permeance of the magnetic core. Is equivalent to 8% or less. Therefore, the permeance relational expression is the following expression (532).

0.08 × Pc ≧ Ps + Pa (532)
When the permeance relational expression is converted into a magnetic resistance relational expression, the following expression (533) is obtained.

... (533)
Further, in the fixing device in the range R3 of this embodiment , the ratio of the magnetic flux passing through the outer route of the conductive layer is 95% or more.

According to Table 2, in the fixing device of the range R3 according to the present embodiment, the ratio of the magnetic flux passing through the outer route of the conductive layer is 94.7% or more, but is 95% in consideration of the measurement error. The ratio of the magnetic flux passing through the outer route of the conductive layer is 95% or more is that the sum of the permeance of the conductive layer and the permeance of the inner side of the conductive layer (the region between the conductive layer and the magnetic core) is the permeance of the magnetic core. Is equivalent to 5% or less. Therefore, the permeance relational expression is the following expression (534).

0.05 × Pc ≧ Ps + Pa (534)
When the permeance relational expression (534) is converted into a magnetic resistance relational expression, the following expression (535) is obtained.

... (535)
By the way, the relational expression of permeance and magnetic resistance is shown for a fixing device in which members in the maximum image area of the fixing device have a uniform cross-sectional configuration in the longitudinal direction. Here, a fixing device in which the members constituting the fixing device in the longitudinal direction have a non-uniform cross-sectional configuration will be described. FIG. 26 includes a temperature detection member 240 inside the conductive layer (region between the magnetic core and the conductive layer). Other configurations are the same as in this embodiment , and the fixing device includes a film 21 having a conductive layer, a magnetic core 22, and a nip portion forming member 24.

  Assuming that the longitudinal direction of the magnetic core 22 is the X-axis direction, the maximum image forming area is a range of 0 to Lp on the X-axis. For example, in the case of an image forming apparatus in which the maximum conveyance area of the recording material is LTR size 215.9 mm, Lp may be 215.9 mm. The temperature detection member 9 is made of a nonmagnetic material having a relative permeability of 1, a cross-sectional area perpendicular to the X axis is 5 mm × 5 mm, and a length parallel to the X axis is 10 mm. It is arranged at a position from L1 (102.95 mm) to L2 (112.95 mm) on the X axis.

  Here, 0 to L1 on the X coordinate are referred to as a region 1, L1 to L2 where the temperature detection member 240 exists are referred to as a region 2, and L2 to LP are referred to as a region 3. A cross-sectional structure in the region 1 is shown in FIG. 27A, and a cross-sectional structure in the region 2 is shown in FIG. As shown in FIG. 27B, since the temperature detecting member 9 is included in the film 21, it is an object of magnetic resistance calculation. In order to perform the magnetic resistance calculation strictly, “magnetic resistance per unit length” is separately obtained for region 1, region 2, and region 3, and integral calculation is performed according to the length of each region. And add them together to obtain the combined magnetoresistance. First, the magnetic resistance per unit length of each component in the region 1 or 3 is shown in Table 4 below.

The magnetic resistance r _c 1 per unit length of the magnetic core in the region 1 is as follows.

r _c 1 = 2.9 × 10 ⁶ [1 / (H · m)]
The magnetic resistance r _a per unit length of the region between the conductive layer and the magnetic core, the unit length of the film guide r _f magnetoresistive r _air units of magnetoresistive conductive layer per length inside of It is the combined magnetoresistance with the punch magnetoresistance. Therefore, it can be calculated using the following equation (536).

... (536)

As a result of the calculation, the magnetoresistance r _a 1 in the region 1 and the magnetoresistance r _s 1 in the region 1 are as follows.

r _a 1 = 2.7 × 10 ⁹ [1 / (H · m)]
r _s 1 = 5.3 × 10 ¹¹ [1 / (H · m)]
Further, since the region 3 is the same as the region 1, it is as follows.

r _c 3 = 2.9 × 10 ⁶ [1 / (H · m)]
r _a 3 = 2.7 × 10 ⁹ [1 / (H · m)]
r _s 3 = 5.3 × 10 ¹¹ [1 / (H · m)]
Next, the magnetic resistance per unit length of each component in the region 2 is shown in Table 5 below.

The magnetic resistance r _c 2 per unit length of the magnetic core in the region 2 is as follows.

r _c 2 = 2.9 × 10 ⁶ [1 / (H · m)]
Magnetoresistive r _a per unit length of the region between the conductive layer and the magnetic core, the magnetic resistance per unit length of the nip forming member r _f, the magnetic resistance per unit length of the thermistor r _t, This is the combined magnetoresistance of the magnetic resistance per unit length of the air r _air inside the conductive layer. Therefore, it can be calculated by the following equation (537).

... (537)
As a result of the calculation, the magnetic resistance r _a 2 per unit length and the magnetic resistance r _c 2 per unit length in the region 2 are as follows.

r _a 2 = 2.7 × 10 ⁹ [1 / (H · m)]
r _s 2 = 5.3 × 10 ¹¹ [1 / (H · m)]
Since the calculation method of area 3 is the same as that of area 1, it is omitted.

The reason why r _a 1 = r _a 2 = r _a 3 in the magnetoresistance r _a per unit length of the region between the conductive layer and the magnetic core will be described.

  In the calculation of the magnetic resistance in the region 2, the cross-sectional area of the thermistor 9 is increased, and the cross-sectional area of air inside the conductive layer is decreased. However, since both have a relative permeability of 1, the magnetic resistance is the same regardless of the presence or absence of the thermistor 9. That is, when only a non-magnetic material is disposed in the region between the conductive layer and the magnetic core, the calculation of the magnetoresistance is sufficient for calculation accuracy even if it is treated the same as air. This is because, in the case of a non-magnetic material, the relative permeability is almost close to 1. On the other hand, in the case of a magnetic material (nickel, iron, silicon steel, etc.), it is better to calculate by dividing a region where the magnetic material is present from other regions.

  The integral of the magnetoresistance R [A / Wb (1 / H)] as the combined magnetoresistance in the busbar direction of the conductive layer is relative to the magnetoresistances r1, r2, r3 [1 / (H · m)] in each region. It can be calculated as the following equation (538).

... (538)
Therefore, the core magnetic resistance Rc [H] in the section from one end to the other end of the maximum conveyance area of the recording material can be calculated as the following equation (539).

・ ・ ・ ・ ・ ・ (539)
In addition, the combined magnetic resistance Ra [H] of the region between the conductive layer and the magnetic core in the section from one end to the other end of the maximum conveyance region of the recording material can be calculated as the following equation (540).

... (540)
The combined magnetic resistance Rs [H] of the conductive layer in the section from one end to the other end of the recording material maximum conveyance area is expressed by the following equation (541).

... (541)
Table 6 below shows the calculation performed in each region.

  From Table 6 above, Rc, Ra, and Rs are as follows.

Rc = 6.2 × 10 ⁸ [1 / H]
Ra = 5.8 × 10 ¹¹ [1 / H]
Rs = 1.1 × 10 ¹⁴ [1 / H]
The combined magnetoresistance Rsa of Rs and Ra can be calculated by the following equation (542).

... (542)
From the above calculation, Rsa = 5.8 × 10 ¹¹ [1 / H], which satisfies the following expression (543).

... (543)
In this way, in the case of a fixing device having a non-uniform cross-sectional shape in the direction of the bus of the conductive layer, it is divided into a plurality of regions in the direction of the bus of the conductive layer, and the magnetoresistance is calculated for each region, Finally, the permeance or magnetoresistance obtained by combining them may be calculated. However, when the target member is a non-magnetic material, the magnetic permeability is substantially equal to the magnetic permeability of air, so that the calculation may be performed assuming that the air is air.

  Next, the parts to be included in the calculation will be described. It is desirable to calculate the permeance or the magnetic resistance for a part that is in the region between the conductive layer and the magnetic core and at least a part of which is in the recording material maximum conveyance region (0 to Lp). Conversely, members placed outside the conductive layer need not calculate permeance or magnetoresistance. This is because, as described above, the induced electromotive force in Faraday's law is proportional to the time change of the magnetic flux penetrating the circuit vertically, and is independent of the magnetic flux outside the conductive layer. In addition, since the member disposed outside the maximum conveyance area of the recording material in the bus line direction of the conductive layer does not affect the heat generation of the conductive layer, it is not necessary to calculate.

[Other embodiments]
In the fixing device 110 of the reference example , the difference between the maximum temperature of the film rotation period described in Example 1 and the reference temperature (average temperature) may be used as the temperature fluctuation amount of the film rotation period. Alternatively, the difference between the lowest temperature and the highest temperature in one rotation period of the film may be used.

In the fixing device 110 according to the first exemplary embodiment , Tpp or t1 described in the reference example may be used as the amount of change in temperature during one rotation period of the film.

Further, in the fixing device 110 of the first embodiment, it is expected that the same temperature measuring element cannot be used at the center and the end in the longitudinal direction of the film 21 due to the convenience of the device. In this case, the film breakage may be detected on the basis of a table or a relational expression, for example, by storing the correspondence between the temperature sensing elements in a memory (not shown) or the like. Or when it comprises so that the temperature of the film 21 may be detected via a certain member, the measurement temperature range by a temperature sensing element differs. In this way, even when the temperature ranges measured by the temperature measuring elements are different, the correspondence between the temperature measuring elements may be stored in a memory (not shown) or the like, and the film breakage may be detected based on a table or a relational expression. Moreover, when detecting the film breakage of less than 4 mm illustrated, it becomes possible by increasing the number of temperature sensing elements.

In the fixing device 110 according to the reference example and the first embodiment , two or more temperature sensing elements are provided at different positions in the longitudinal direction of the films 1 and 21, and the results of the detected temperatures of these temperature sensing elements are compared to compare the rotation period of the film 1 The amount of temperature fluctuation may be obtained.

In the fixing device 110 of the reference example and the first embodiment , the temperature measuring elements 9, 10, and 11 are not limited to the non-contact type thermistor, and a contact type thermistor may be used. The non-contact type thermistor and the contact type thermistor may be inside the films 1 and 21.

  In addition, in the case where the peripheral speeds of the films 1 and 21 are high, it is expected that the temperature fluctuation amount in one rotation period of the film cannot be accurately detected from the viewpoint of the responsiveness of the temperature measuring elements 9, 10, and 11. . In this case, the films 1 and 21 may be rotated at a speed slower than the rotation speed during normal image formation, and the processing of Step 1-1 to Step 1-8 described above may be performed.

  Generally, film breakage may occur when a recording material remaining in the fixing device due to a jam or the like is removed by an unexpected method. Therefore, when the fixing device 110 is taken in and out of the image forming apparatus 100, or when the operation of the apparatus is confirmed immediately after the image forming apparatus is turned on, the processing of Step 1-1 to Step 1-8 is performed in a short time. Thus, it is more desirable to use the apparatus if film breakage is detected before the actual printing operation.

In the fixing device 110 of the reference example , when the film temperature is broken and the surface temperature fluctuates over the entire length of the film 1, the temperature control element 9 for temperature control also detects the temperature fluctuation. Therefore, as shown in FIG. 5, after the fixing device 110 reaches the temperature control target temperature, the temperature fluctuation in one rotation period of the film may increase. In such a case, the predetermined value of the rotation period of the film for determining whether or not the film is broken may be changed when the fixing device 110 is started up and after the temperature adjustment target temperature is reached.

In the reference example and the first embodiment , the film breakage detection sequence when starting up the fixing device 110 before reaching the temperature adjustment target temperature has been described. The timing at which the film breakage detection sequence is executed is not limited to this, and may be when the recording material P passes through the fixing device 110 or when the recording material P during paper passing does not pass through the fixing device 110. Here, the time when the recording material P passes through the fixing device 110 refers to the time when the toner image T is heated and fixed while the recording material P is conveyed through the nip portion N. The time when the recording material P is not passing through the fixing device 110 during the passage of paper refers to the interval between the recording material between the preceding recording material and the succeeding recording material that are continuously introduced into the nip portion.

In the reference example and the fixing device 110 according to the first embodiment, the example in which the films 1 and 21 are used as the cylindrical rotating body has been described. However, the thickness of the heat generating layers 1a and 21a or the elastic layers 1b and 21b is replaced with the film. A thicker so-called fixing roller may be used.

In the fixing device 110 of the reference example , the flange members 12a and 12b are brought into contact with both ends of the film 1 and an alternating current is passed through the flange member in the direction of the rotation axis X of the film, whereby the film generates heat. did. As a modification of the fixing device 110, there is also a fixing device that applies a direct current in the direction of the rotation axis X of the film through the flange members 12a and 12b brought into contact with both ends of the film 1. FIG. 17 is a diagram for explaining a phenomenon in which the temperature fluctuates in one rotation period of the film when the film is broken in the fixing device that applies a direct current to the film 1. In FIG. 17, illustration of the flange members 12a and 12b is omitted.

In the fixing device 110 of the reference example , when the time average of the rotation period of the film 1 of the film 1 in FIGS. 6C and 6D is averaged, the current density is sparse in the entire length of the film where the film is broken. The temperature fluctuation of one rotation period of the film occurred in the entire length of the film.

On the other hand, in a fixing device that applies a direct current to the film 1, current flows in the film 1 only in one direction as shown in FIG. Therefore, as shown in FIG. 17B, when film breakage occurs, a current density density state occurs only in a region after the current bypasses the film breakage end B and the film breakage end C. Therefore, similarly to the fixing device 110 of the reference example , the film temperature is not affected by the damage at a position sufficiently separated in the longitudinal direction of the film 1 from the location where the film breakage has occurred.

In such a case, as in Example 1 , the amount of change in the temperature of one rotation period of the film is monitored based on the detected temperature of each of the temperature measuring elements 9, 10, 11 arranged in the longitudinal direction of the film 21. Then, when the fluctuation amount of the temperature in one rotation period of the film is larger than a predetermined value, it may be determined that the film is broken.

1, 25: Pressure roller, 9, 10, 11: Temperature detecting element, 12a, 12b: Flange member, 22: Magnetic core, 23: Excitation coil, 100A: Image forming unit, 110: Fixing unit , N: nip portion, P: recording material, Tpp, t1: amount of temperature fluctuation in one rotation period of film, X: rotation axis of film

Claims (9)

A cylindrical rotating body having a conductive layer, and an alternating body that is arranged inside the rotating body and has a spiral-shaped portion whose spiral axis is substantially parallel to the generatrix direction of the rotating body, and causes the conductive layer to generate electromagnetic induction heat. A coil for forming a magnetic field, a magnetic core disposed along the generatrix direction in the spiral-shaped part, for inducing magnetic lines of the alternating magnetic field, and a pressure forming a nip part together with the rotating body A fixing device for fixing the image to the recording material by heating while conveying the recording material carrying the image at the nip portion,
The magnetic core is made of a ferromagnetic material and has a shape that does not form a loop outside the rotating body,
The sum of the permeance of the conductive layer and the permeance of the region between the conductive layer and the magnetic core is 28% or less of the permeance of the magnetic core;
Wherein a rotator temperature detecting member for detecting the temperature of the fluctuation amount of the rotating body 1 rotation period of the detected temperature of said temperature detecting member is stopped a predetermined amount larger field case, energization of the rotary body A fixing device. A cylindrical rotating body having a conductive layer, and an alternating body that is arranged inside the rotating body and has a spiral-shaped portion whose spiral axis is substantially parallel to the generatrix direction of the rotating body, and causes the conductive layer to generate electromagnetic induction heat. A coil for forming a magnetic field, a magnetic core disposed along the generatrix direction in the spiral-shaped part, for inducing magnetic lines of the alternating magnetic field, and a pressure forming a nip part together with the rotating body A fixing device for fixing the image to the recording material by heating while conveying the recording material carrying the image at the nip portion,
The magnetic core is made of a ferromagnetic material and has a shape that does not form a loop outside the rotating body,
The sum of the permeance of the conductive layer and the permeance of the region between the conductive layer and the magnetic core is 28% or less of the permeance of the magnetic core;
The has a temperature detecting member for detecting a temperature of the rotating body, said temperature sensing member of sensing a temperature rotary body 1 rotation period fluctuation amount is a predetermined amount larger than the field case of fixing device, characterized in that for informing abnormality .   The fixing device according to claim 1, wherein the fluctuation amount is a difference between a maximum temperature and a reference temperature during a period in which the rotating body rotates once.   The fixing device according to claim 1, wherein the fluctuation amount is a difference between a maximum temperature and a minimum temperature during a period in which the rotating body rotates once.   The fixing device according to claim 1, wherein the fluctuation amount is a time during which a low temperature is maintained with respect to a reference temperature during a period in which the rotating body rotates once.   6. The apparatus according to claim 1, wherein the variation amount is obtained by comparing at least two temperature detection members and comparing the detection temperature results of the two or more temperature detection members. The fixing device according to Item.   The temperature detection member is provided in plurality, and each of the plurality of temperature detection members detects temperatures at different positions in the direction of the rotation axis of the rotating body. The fixing device according to one item.   2. The rotating body generates heat when an electrode member is brought into contact with both end portions of the rotating body and a current is passed through the electrode member in a direction of a rotation axis of the rotating body. The fixing device according to claim 7. In an image forming apparatus having an image forming unit that forms an image on a recording material, and a fixing unit that fixes an image formed on the recording material to the recording material.
An image forming apparatus comprising: a fixing device according to any one of claims 1 to 8 as the fixing unit.